Roll

ABSTRACT

A roll has a base material layer, a front surface layer, and stress relaxation layer. The base material layer is made of low hardness rubber material and provided on an outer circumference of a metal core. The stress relaxation layer is provided on the base material layer and made of material which is at least higher in hardness than the base material layer and larger in stretch than the front surface layer. The front surface layer is made of resin material and provided on the stress relaxation layer. The stress relaxation layer is made of rubber material containing self-crosslinking resin. The stress relaxation layer has a thickness in a range of from 5 to 50 μm, and stress not lower than 5 MPa at 10% stretch.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to rolls to be used in copying machines orprinters, and particularly to conductive rolls to be provided around aphotoconductor drum.

2. Description of the Related Art

In a copying machine or a printer, an electrostatic latent image formedon a photoconductor drum is developed by toner (developer) fed from adeveloping roll. The toner image on the photoconductor drum istransferred to a transfer roll. The toner image is then transferred to arecording paper. Then, the recording paper is heated and pressed so thata picture image is formed on the recording paper. Such a roll as used ina copying machine or printer is generally has a structure in which anouter circumference of pipe-like core made of metal such as aluminum oriron is coated with rubber or resin material.

With reduction in hardness of such rolls, particularly, such conductiverolls including a charge roll, a developing roll, and a transfer rollwhich are used around a photoconductor drum, the roll is required tohave high releasability to prevent the toner (developer) from adhering,for the purpose of ensuring nipping property between the roll and thephotoconductor drum. Generally, each of the rolls such as conductiverolls adopts a structure to have a base material layer made of lowhardness rubber material and provided on an outer circumference of ametal core, and a front surface layer made of resin material andprovided on the base material layer.

As the rubber material constituting the base material layer of such aroll, low hardness rubber in which a softening agent such as oil isadded to general-purpose rubber such as NBR or silicon rubber, or foamedrubber of polyurethane has been used. Especially silicon rubber has beenused in view of stability in resistance value. As the resin materialconstituting the front surface layer, resin material have been usedwhich is high in releasability, such as fluororesin, acrylate resin,urethane resin, or silicon resin.

The conductive rolls to be provided around a photoconductor drum aregenerally used with a difference in peripheral velocity between eachconductive roller and the photoconductor drum due to the function of theconductive rollers. Especially, in the developing roller, taking thecarrying quantity and developing property of toner into consideration,it is general to provide a peripheral velocity difference so that theperipheral velocity of the developing roll is about 1.1 times-1.5 timesas large as the peripheral velocity of the photoconductor drum. Further,although it is general to particularly provide no peripheral velocitydifference between the charge roll or the transfer roll and thephotoconductor drum, there occurs actually a peripheral velocitydifference in some degree due to variations in outer diameter of eachroll per se.

Further, in the rolls other than the conductive rolls used around thephotoconductor drum, for example, in the carrying rolls for carryingrecording paper or in the fixing rolls, each roll is rotating in such acondition that a pair of rolls opposed to each other, that is, a roll inquestion and another roll which is a matter to be opposed to each other,are disposed to be in contact with each other. Accordingly, even if anyperipheral velocity difference is not particularly provided between therolls opposed to each other, it can be said that there exists, in fact,a certain amount of peripheral velocity difference between the thusopposed rolls.

If any peripheral velocity difference exists between a roll and a matteropposed to the roll, for example, in a case where a photoconductor drumis disposed as the matter opposed to the roll in question, it is apt togenerate ripple-like deformation called wrinkles in the surface of theroll in question in the rotation driving. It is considered that suchwrinkles are generated as follows. That is, as stated above, the roll isconstituted by a base material layer of low hardness rubber materialprovided on the outer circumference of a metal core and a front surfacelayer of resin material provided on the base material layer.Accordingly, the soft base material layer is deformed by a peripheralvelocity difference between the roll and a matter opposed to the roll inquestion, so that the deformation causes plastic deformation on theupper front surface layer.

As a method of preventing such ripple-like wrinkles from generating, itis considered that the front surface layer is made of a soft material,or the base material layer is made hard. However, when the front surfacelayer is made of a soft material, the lowering of the releasability iscaused so that the function to be required originally cannot besatisfied. Further, the lowering of the releasability causes adisadvantage called filming due to adhesion of toner in the case wherethe roll in question is a developing roll. If the base material layer ismade hard, on the contrary, it becomes difficult to ensure a sufficientnip width between the roll and an opposed matter such as aphotoconductor drum. Accordingly, it is necessary to provide acountermeasure to heighten the accuracy of size of the roll in questionper se so that a predetermined nip width can be obtained stably.

Further, in a case of a transfer roll which requires a certain nipwidth, generally, the roll in question could not help taking a soft rollstructure at the sacrifice of the releasability. In addition to theproblem of generation of ripple-like wrinkles, it is the existingcondition that the mechanism has to be complex because a cleaning memberis required to be provided to remove surplus toner adhering onto theroll surface.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a roll which can securenecessary nip properties and releasability, and at the same time, theroll in question does not generate ripple-like wrinkles in the frontsurface layer even if there exists a peripheral velocity differencebetween the roll in question and any other opposed matter such as aphotoconductor drum.

In order to achieve the object, according to the invention, there isprovided a roll including: a base material layer made of low hardnessrubber material and provided on an outer circumference of a metal core;and a front surface layer made of resin material and provided on thebase material layer; wherein a stress relaxation layer is providedbetween the base material layer and the front surface layer, the stressrelaxation layer being made of material which is at least higher inhardness than the base material layer and larger in stretch than thefront surface layer.

In the roll of the invention, specifically, the base material layer ismade of rubber material with low hardness not higher than 25 degrees inJIS-A hardness, the front surface layer is made of resin material notlarger than 30% in stretch, and the stress relaxation layer is made ofmaterial having stress not lower than 5 MPa at 10% stretch.

In the roll of the invention, the stress relaxation layer is made ofrubber material added with at least one kind of self-crosslinking resinsuch as blocked type self-crosslinking isocyanate resin, blocked typeself-crosslinking epoxy resin, and blocked type self-crosslinkingphenolic resin. The loading of the self-crosslinking resin to the rubbermaterial is 20-150 parts by weight relative to 100 parts by weight ofthe rubber material.

In the roll according to the invention, the stress relaxation layer hasa thickness in a range of from 5 to 50 μm. In the roll according to theinvention, preferably, the base material layer has a thickness notsmaller than 3 mm, and the roll according to the invention is suitableas a conductive roll having roll hardness not higher than 60 degrees inAsker-C hardness at a load of 1 kg.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing a roll of the present invention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

According to the invention, in a roll having a base material layer madeof low hardness rubber material on an outer circumference of a metalcore, and a front surface layer relatively hard and made of resinmaterial on the base material layer, there is provided at least a stressrelaxation layer between the base material layer and the front surfacelayer. This stress relaxation layer is made of material which is higherin hardness than the base material layer and larger in stretch than thefront surface layer. For example, the stress relaxation layer is made ofrubber material added with resin. Incidentally, any layer other than thestress relaxation layer may be provided between the base material layerand the front surface layer for performing any other function, ifnecessary.

For example, FIG. 1 is a sectional view showing such a roll of theinvention. In FIG. 1, a base material layer 2 is disposed on a metalcore 1. A stress relaxation layer 3 is disposed on the base material 2.A front surface layer 4 is disposed on a stress relaxation layer.

Particularly, conductive rolls, such as a charge roll, a developingroll, and a transfer roll, are used around a photoconductor drum.Specifically, each roll is configured so as to have a base materiallayer made of rubber material with low hardness not higher than 25degrees in JIS-A hardness, and a front surface layer made of resinmaterial not larger than 30% in stretch. In this case, as a stressrelaxation layer, it is preferable to use material having stress notlower than 5 MPa at the time of 10% stretch.

Further, the “stretch” of the stress relaxation layer or the frontsurface layer means “stretch” at the time of cut off as defined in theJIS K6251. Further, the “stress” at the time of 10% stretch of thestress relaxation layer is the “stress” imposed on the material of thelayer in question when the material is stretched by 10%, and designatesthe “stress” at the time of 10% stretch defined in JIS K6251.

When a stress relaxation layer is provided between a base material layerand a front surface layer in a roll in such a manner, ripple-likewrinkles can be prevented from generating in the front surface layer ofthe roll, even if a peripheral velocity difference exists between theroll in question and an opposed matter such as a photoconductor drum.This is because the stress relaxation layer made of material which ishigher in hardness than the base material layer and which is larger instretch than the front surface layer scatters and relaxes thedeformation of the base material layer so that the deformation can beprevented from being transferred to the front surface of the roll.Further, in the roll according to the invention, the stress relaxationlayer does not spoil the low hardness of the roll as a whole, so that anecessary nip width can be ensured between the roll in question andanother roll such as a photoconductor drum. Further, the roll isprovided with the front surface of resin material, so that the rollkeeps releasability enough to prevent adhesion of toner.

As the material forming the stress relaxation layer, general-purposerubber material such as nitrile-butadiene rubber (NBR), hydrogenatednitrile-butadiene rubber (H-NBR), hydrin rubber (CHC), orethylene-propylene rubber (EPDM), added with resin, can be used. Forexample, such rubber material added with at least one kind ofself-crosslinking resin such as blocked type self-crosslinkingisocyanate resin, blocked type self-crosslinking epoxy resin and blockedtype self-crosslinking phenolic resin can be used. Incidentally, suchself-crosslinking resin is available commercially, for example, in thetrade name of DB980K from DAINIPPON INK AND CHEMICALS, INC.

The loading of the self-crosslinking resin to the rubber material ispreferably 20-150 parts by weight relative to 100 parts by weight of therubber material, and more preferably 50-100 parts by weight likewise. Ifthe loading of the self-crosslinking resin is lower than 20 parts byweight relative to 100 parts by weight of the rubber material, it isimpossible to obtain the effect that the stretch of the rubber materialis suppressed by the addition of the resin, to say it specifically, itis impossible to obtain material that is not lower than 5 MPa in stressat the time of 10% stress. On the contrary, if the loading of theself-crosslinking resin exceeds 100 parts by weight relative to 100parts by weight of the rubber material, the hardness becomes too high asrubber material. Thus, it becomes difficult to secure a sufficient nipwidth because the flexibility of the roll is impaired.

The thickness of the stress relaxation layer is preferably in a range offrom 5 to 50 μm, more preferably in a range of from 15 to 35 μm. If thestress relaxation layer is thinner than 5 μm, not only is it difficultto make the thickness uniform, but it is also impossible for the stressrelaxation layer to play its part to scatter and relax the deformationof the base material layer. On the contrary, if the stress relaxationlayer is thicker than 50 μm, it becomes, unfavorably, difficult tosecure a sufficient nip width because the flexibility of the roll isimpaired.

Ripple-like wrinkles described above will be generated more easily ifthe base material layer is thicker, specifically when the base materiallayer is not thinner than 3 mm. In each of rolls according to theinvention, however, even if the base material layer is not thinner than3 mm, it is possible to prevent such ripple-like wrinkles from beinggenerated. In addition, in each of conductive ones of the rollsaccording to the invention, it is desirable that the roll hardness ofthe whole roll provided with the stress relaxation layer is kept nothigher than 60 degrees in Asker-C hardness (load 1 kg).

EXAMPLE

A pipe of SUM22 measuring 10 mm in diameter by 250 mm in length wassubjected to electroless nickel plating so as to form a metal core. Abonding agent was applied to the outer circumferential surface of themetal core. After that, the metal core was disposed in a mold whoseinner-diameter shape was cylindrical with a diameter of 20 mm and whichwas split into two parts, that is, upper and lower parts. Silicon rubberwas injected and charged into an air gap between the metal core and theinner-diameter portion of the mold, and then vulcanized and molded at170° C. for 30 minutes. After that, the metal core was released andextracted from the mold. A rubber layer formed on the outercircumference of the metal core was surface-polished by a cylindricalpolishing machine. Thus, a base material layer made of silicon rubberwhich was 20 mm in diameter (5 mm in thickness) and 10 degrees in JIS-Ahardness was obtained.

Next, as shown in the following Table 1, the indicated loadings of partsby weight of self-crosslinking resins were added and mixed to 100 partsby weight of each rubber material. The surface of the base materiallayer formed on each metal core as described above was coated with theobtained rubber material in a dipping method, and then subjected tovulcanization reaction at 190° C. for 60 minutes, so as to form a stressrelaxation layer. Each stress relaxation layer obtained thus was coatedwith acrylate resin of 14% stretch in a similar dipping method, andhardened at 140° C. so as to form a front surface layer 5 μm thick andmade of acrylate resin.

As for each roll obtained thus, roll hardness (Asker-C hardness at aload of 1 kg) was obtained, and generation of wrinkles in the frontsurface layer was evaluated. That is, each sample of rolls was pressedonto a metal roll having a diameter of 30 mm at a load of 500 gf in oneend, and both the rolls were driven to rotate continuously for 24 hourswith a peripheral velocity difference of 1.2 times between the metalroll and each sample of rolls. After that, the presence/absence ofwrinkles in the front surface layer was checked. These results are showntogether in the following Table 1.

Sample 1 2 3 4 5 6 7 8 9 stress rubber H-NBR H-NBR H-NBR H-NBR NBR CHCnone H-NBR H-NBR relaxation material layer self- isocyanate isocyanateepoxy phenol isocyanate isocyanate none none none cross- linking resinparts by weight 50 100  75 75 75 75 — — — of added resin layer 30 30 2533 28 34 — 32 27 thickness (μm) at 10% stretch  8 12  6 21  7 13 —  21.1 (MPa) roll hardness 48 52 44 53 46 50 31 38 35 (Asker-C) generationof No No No No No No Yes Yes Yes wrinkles on front surface layer

As is understood from Table 1, in each of Sample 7 having no stressrelaxation layer and Samples 8 and 9 whose stress relaxation layers weremade of only general-purpose rubber material, the roll hardness could bekept low, but generation of ripple-like wrinkles was confirmed in thefront surface layer after the continuous rotation with a peripheralvelocity difference. On the other hand, in each of rolls in Samples 1 to6 according to the invention, no generation of wrinkles was confirmed,and the roll hardness could be kept within a range required as aconductive roll.

According to the invention, rolls for use in a copying machine or aprinter can be provided as follows. That is, in each roll, a stressrelaxation layer is provided between its base material layer made ofrubber material and its front surface layer made of resin material.Thus, even if there is a difference in peripheral velocity between theroll and an opposed matter such as a photoconductor drum, there is nofear that ripple-like wrinkles are generated in the front surface layer.In addition, the roll according to the invention can keep roll hardnesslow enough to secure necessary nip properties while keepingreleasability high due to the front surface layer. Accordingly, the rollaccording to the invention is effective particularly as a conductiveroll used around a photoconductor drum, such as a charge roll, adeveloping roll, or a transfer roll.

What is claimed is:
 1. A roll comprising: a metal core; a base materiallayer made of rubber material, the base material layer provided on anouter circumference of the metal core; a stress relaxation layerprovided on the base material layer; and a front surface layer made ofresin material, the front surface layer provided on the stressrelaxation layer, wherein the stress relaxation layer is made ofmaterial being higher in hardness than the base material layer andlarger in stretch than the front surface layer, and the stressrelaxation layer is made of rubber material containingonself-crosslinking resin selected from a group consisting of blockedself-crosslinking isocyanate resin, blocked self-crosslinking epoxyresin, and blocked self-crosslinking phenolic resin.
 2. The rollaccording to claim 1, wherein the base material layer is made of rubbermaterial with low hardness not higher than 25 degrees in JIS-A hardness;the front surface layer is made of resin material not larger than 30% instretch; and the stress relaxation layer is made of material havingstress not lower than 5 MPa at 10% stretch.
 3. The roll according toclaim 1, wherein the rubber material contains 20-150 parts by weight ofthe self-crosslinking resin relative to 100 parts by weight of therubber material.
 4. The roll according to claim 1, wherein the stressrelaxation layer has a thickness in a range of from 5 to 50 μm.
 5. Theroll according to claim 1, wherein the base material layer has athickness not smaller than 3 mm.
 6. The roll according to claim 1, beinga conductive roll having roll hardness not higher than 60 degrees inAsker-C hardness at a load of 1 kg.